Engine lubricating device

ABSTRACT

An engine lubrication system having a lubricating oil pump that is rotationally driven by a crankshaft to send under pressure a lubricating oil to a part needing to be lubricated, characterized in that the lubricating oil pump is disposed so as to be connected to an end of a crankshaft in such a manner that a pump shaft aligns with the crankshaft substantially coaxially, in that an in-pump oil supply passageway is formed in the lubricating oil pump in such a manner as to pass therethrough from a side opposite to the crankshaft to a side of the crankshaft, and in that the in-pump oil supply passageway so formed is made to communicate at one end thereof with an in-crankshaft oil supply passageway formed in the crankshaft for supplying a lubricating oil to a part of the crankshaft which needs to be lubricated and is made to communicate at the other end thereof with a discharge port of the lubricating oil pump via a lubricating oil passageway.

TECHNICAL FIELD

The present invention relates to an engine lubrication system having alubricating oil pump that is rotationally driven by a crankshaft to sendunder pressure lubricating oil to parts needing to be lubricated.

BACKGROUND ART

Conventionally, as engine lubrication systems, there exist for example,an engine lubrication system as disclosed in JP-A-10-339124 in which alubricating oil pump is directly attached to an end of a crankshaft andan engine lubrication system as disclosed in JP-UM-A-5-52205 in which alubricating oil pump is disposed at an end of a crankshaft with a pumpshaft of the pump being connected to the crankshaft via a couplingpiece.

In the lubrication system in which the lubricating oil pump is directlyconnected to the end of the crankshaft, in the event that the center ofthe crankshaft oscillates, this constitutes a direct cause of the swayof an inner rotor of the lubricating oil pump, leading to the reductionin durability of the lubricating oil pump. Due to this, the lubricatingoil pump needs to be disposed at a position as close to a bearingportion of the crankshaft as possible, and hence there is caused aproblem of narrowing the degree of freedom in selecting where to disposethe lubricating oil pump.

In addition, in the lubrication system in which the crankshaft and thepump shaft are connected together with the coupling piece, since adischarge port of the pump is made to communicate directly with an oilsupply passageway formed in the coupling piece along the axial centerthereof, there is caused a problem that an oil filter is difficult to bedisposed on a discharge side of the lubricating pump.

The invention was made in view of the problems inherent in theconventional systems, and an object thereof is to provide an enginelubrication system which can avoid the influence of the deflection ofthe crankshaft, which can enhance the degree of freedom in selectingwhere to dispose a lubricating oil pump and which has a high degree offreedom in design where, for example, an oil filter is disposed on adischarge side of the lubricating oil pump.

DISCLOSURE OF THE INVENTION

According to a first aspect of the invention, there is provided anengine lubrication system having a lubricating oil pump that isrotationally driven by a crankshaft to send under pressure a lubricatingoil to a part needing to be lubricated, characterized in that thelubricating oil pump is disposed so as to be connected to an end of acrankshaft in such a manner that a pump shaft aligns with the crankshaftsubstantially coaxially, in that an in-pump oil supply passageway isformed in the lubricating oil pump in such a manner as to passtherethrough from a side opposite to the crankshaft to a side of thecrankshaft, and in that the in-pump oil supply passageway so formed ismade to communicate at one end thereof with an in-crankshaft oil supplypassageway formed in the crankshaft for supplying a lubricating oil to apart of the crankshaft which needs to be lubricated and is made tocommunicate at the other end thereof with a discharge port of thelubricating oil pump via a lubricating oil passageway.

According to a second aspect of the invention, there is provided anengine lubrication system as set forth in the first aspect of theinvention, characterized in that the in-pump oil supply passageway isformed in the pump shaft, in that the pump shaft and the crankshaft areconnected together with a coupling which can absorb a displacement ofthe shafts in a direction normal thereto, in that a connecting pipe isinterposed between the pump shaft and the crankshaft in such a manner asto absorb the displacement of the shafts in the direction normalthereto, and in that the in-crankshaft oil supply passageway and thein-pump oil supply passageway are made to communicate with each other bythe connecting pipe.

According to a third aspect of the invention, there is provided anengine lubrication system as set forth in the first or second aspect ofthe invention, characterized in that the lubricating oil pump isattached to a crankcase cover detachably and is covered with a pumpcover that is attached to the crankcase cover detachably.

According to a fourth aspect of the invention, there is provided anengine lubrication system as set forth in the third aspect of theinvention, characterized in that an oil filter is provided at anintermediate position along the length of the lubricating oilpassageway, in that the oil filter is constructed such that an elementis disposed in a filter compartment defined by the crankcase cover and afilter cover attached to the crankcase cover detachably, in that a partof the lubricating oil passageway situated between the discharge port ofthe lubricating oil pump and the oil filter is formed on the crankcasecover, and in that a part of the lubricating oil passageway situatedbetween the oil filter and the in-pump passageway is formed on thefilter cover which covers the oil filter detachably.

According to a fifth aspect of the invention, there is provided anengine lubrication system as set for thin the fourth aspect of theinvention, characterized in that the pump cover and the filter cover areintegrally formed.

According to a sixth aspect of the invention, there is provided anengine lubrication system as set forth in the fourth or fifth aspect ofthe invention, characterized in that a passageway on a pick-up side ofthe lubricating oil pump and a part of the lubricating oil passagewaythat is situated on a downstream side of the oil filter are made tocommunicate with each other via a pressure regulating relief valve.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a right-hand side view of an engine according to an embodimentof the invention.

FIG. 2 is a sectional plan view showing a development of the engine.

FIG. 3 is a left-hand side view showing a valve train device of theengine.

FIG. 4 is a sectional rear elevation of the valve train device.

FIG. 5 is a sectional plan view showing a development of a balance shaftof the engine.

FIG. 6 is a bottom view of a cylinder head of the engine.

FIG. 7 is a bottom view of a cylinder body of the engine.

FIG. 8 is a sectional side view showing a portion where the cylinderhead of the engine is connected to the cylinder body.

FIG. 9 is a sectional side view showing a portion where the cylinderbody of the engine is connected to the crankcase.

FIG. 10 is another sectional side view showing a portion where thecylinder body of the engine is connected to the crankcase.

FIG. 11 is a left-hand side view showing a balancer unit of the engine.

FIG. 12 is an enlarged cross-sectional view of a portion where a holdinglever of the balancer unit is attached.

FIG. 13 is a side view of constituent components of a rotational leverof the balancer unit.

FIG. 14 is a side view showing a damping construction of a balancerdrive gear of the balancer unit.

FIG. 15 is a right-hand side view of the balancer unit.

FIG. 16 is a sectional right-hand side view of a bearing bracket of theengine.

FIG. 17 is a sectional left-hand side view of a bearing bracket.

FIG. 18 is an explanatory drawing showing the construction of alubrication system of the engine.

FIG. 19 is a drawing showing the construction of the lubrication system.

FIG. 20 is a sectional side view of an area surrounding a lubricatingoil pump of the lubrication system.

FIG. 21 is a sectional left-hand side view of the lubrication system.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the invention will be described withreference to the accompanying drawings.

FIGS. 1 to 21 are drawings for describing an embodiment of theinvention. In the drawings, reference numeral 1 denotes a water-cooled,4-cycle, single cylinder, 5-valve engine, and in general, the engine hasa construction in which a cylinder body 3, a cylinder head 4 and acylinder head cover 5 are stacked on and fastened to a crankcase 2, anda piston 6 slidably disposed in a cylinder bore 3 a in the cylinder body3 is connected to a crankshaft 8 via a connecting rod 7.

The cylinder body 3 and the crankcase 2 are securely connected togetherby screwing four case bolts 30 a which pass through a lower flangeportion (a case side flange portion) 3 b into a cylinder side matingsurface 2 e of the crankcase 2. To be more specific, the case bolts 30 aare screwed into bolt connecting portions (connecting boss portions) 12c of iron alloy bearing brackets 12, 12′ (which will be described lateron) embedded in left and right wall portions of the aluminum alloycrankcase 2, respectively, through insert casting. Note that referencenumeral 31 a denotes a positioning dowel pin for positioning thecrankcase 2 and the cylinder body 3.

In addition, the cylinder body 3 and the cylinder head 4 are connectedtogether with two short head bolts 30 b and four long head bolts 30 c.The short head bolt 30 b is screwed to be planted in a portion below aninduction port 4 c and a portion below an exhaust port in the cylinderhead 4, extends downwardly to pass through an upper flange portion 3 fof the cylinder block 3 and protrudes downwardly therefrom. Then, a capnut 32 a is screwed on the downwardly protruding portion of the shorthead bolt 30 b, whereby the upper flange portion 3 f and hence thecylinder body 3 are fastened to a cylinder side mating surface 4 a ofthe cylinder head 4.

In addition, the long head bolt 30 c is screwed to be planted in thelower flange portion 3 b of the cylinder body 3, extends upwardly topass from the upper flange portion 3 f of the cylinder block 3 through aflange portion 4 b of the cylinder head 4 and protrudes upwardlytherefrom. Then, a cap nut 32 b is screwed on the upwardly protrudingportion of the long head bolt 30 c, whereby the lower flange portion 3 band hence the cylinder body are fastened to the cylinder side matingsurface 4 a of the cylinder head 4.

Thus, in connecting the cylinder body 3 and the cylinder head 4together, since not only the upper flange portion 3 f of the cylinderbody 3 is fastened to be fixed to the cylinder head 4 with the shorthead bolts. 30 b and the cap nuts 32 but also the long head bolts 30 care planted in the lower flange portion 3 b which is fastened to besecurely connected to the mating surface 2 e of the crankcase 2, so thatthe cylinder body 3 is fastened to be fixed to the flange portion 4 b ofthe cylinder head 4 with the long head bolts 30 c and the cap nuts 32 b,a tensile load generated by a combustion pressure comes to be borne bythe cylinder body 3 and the four long head bolts 30 c, so that a loadapplied to the cylinder body 3 can be reduced accordingly or by such anextent that the load is so borne by the cylinder body 3 and the longhead bolts 30 c. As a result, a stress generated at, in particular, anaxially intermediate portion of the cylinder body 3 can be reduced,thereby making it possible to secure a required durability even in casethe thickness of the cylinder body 3 is reduced.

Incidentally, in the event that only the upper flange portion 3 f of thecylinder body 3 is connected to the cylinder head 4, an excessivelylarge tensile stress is generated at the axially intermediate portion ofthe cylinder body 3, and in an extreme case, there occurs a concern thata crack is generated at the portion in question. In the embodiment,however, the generation of the excessively large stress at theintermediate portion of the cylinder body can be avoided due to thepresence of the long head bolts 30 c, thereby making it possible toprevent the generation of a crack.

In addition, in planting the long head bolts 30 c in the lower flangeportion 3 b, since the long head bolts are disposed in the vicinity ofthe crankcase fastening case bolts 30 a, respectively, the loadgenerated by the combustion pressure can be transmitted from thecylinder head 4 to the crankcase 2 via the long head bolts 30 c and thecylinder body in an ensured fashion, thereby making it possible toimprove the durability against the load in this respect.

Here, the right-side bearing bracket 12′ has, as shown in FIGS. 5, 16, aboss portion 12 b in which the right-side bearing 11 a′ of thecrankshaft 8 is inserted to be fitted in the bearing hole 12 a throughpress fit. Then, the bolt connecting portions 12 c, 12 c extend upwardlyfrom front and rear portions which hold the crankshaft 8 therebetween asseen in a direction in which the crankshaft 8 extends to the vicinity ofthe cylinder-side mating surface of the crankcase 2.

In addition, in the left-side bearing bracket 12, as shown in FIGS. 5,17, the bolt connecting portions 12 c, 12 c extend from front and rearportions which hold the crankshaft 8 therebetween as seen in thedirection in which the crankshaft 8 extends to the vicinity of thecylinder-side mating surface 2 e of the crankcase 2. In addition, acollar hole 12 e is formed in the boss portion 12 b into which an ironbearing collar 12 d having an outside diameter larger than that of abalancer driving gear 25 a, which will be described later on, is pressfitted. And, a left-side crankshaft bearing la is inserted to be fittedin the bearing hole 12 a of the bearing collar 12 d.

Here, the bearing collar 12 d is provided to facilitate the assembly ofthe crankshaft 8 in the crankcase 2 with a gear unit 25 having thebalancer driving gear 25 a being press fitted on the crankshaft 8.

In addition, as shown in FIG. 5, a seal plate 25 d is interposed betweenthe gear unit 25 on a left shaft portion 8 c of the crankshaft 8 and thebearing 11 a. An inside diameter side portion of the seal plate 25 d isheld by the gear unit 25 and an inner race of the bearing 11 a, and aslight gap is provided between an outside diameter side portion thereofand an outer race of the bearing 11 a for avoiding the interferencetherebetween. In addition, an inner circumferential surface of a flangeportion 12 h of the bearing collar 12 d is brought into sliding contactwith an outer circumferential surface of the seal plate 25 d.

Furthermore, a seal tube 17 i is interposed between the bearing 11 a′ ofa right shaft portion 8 c′ of the crankshaft 8 and a cover plate 17 g.An inner circumferential surface of the seal tube 17 i is fixedly fittedon the right shaft portion 8 c′. In addition, a seal groove having alabyrinth construction is formed in an outer circumferential surface ofthe seal tube 17 i, and the outer circumferential surface of the sealtube 17 i is brought into sliding contact with an inner circumferentialsurface of a seal bore 2 p formed in the right case portion 2 b.

Thus, the leakage of pressure within a crank compartment 2 c isprevented by interposing the seal plate 25 d and the seal tube 17 i onthe outside of the bearings 11 a, 11 a′ of the left- and right-sidebearing portions 8 c, 8 c′ of the crankshaft 8, respectively.

Thus, according to the embodiment, since the bolt connecting portions(connecting boss portion) 12 c, 12 c which extend toward the cylinderbody 3 side are formed integrally on the both sides across a cylinderbore axis A of each of the crankshaft supporting bearing members 12, 12′of an iron alloy which are cast in the crankcase 2 of an aluminum alloyand the case bolt 30 a for connecting the cylinder body 3 to thecrankcase 2 is screwed into the bolt connecting portion 12 c, the loaddue to the combustion pressure can uniformly borne by the two front andrear bolt connecting portions 12 c which are disposed across thecylinder bore axis A, thereby making it possible to increase theconnecting rigidity between the cylinder body 3 and the crankcase 2.

In addition, since the balance shafts 22, 22′, which are disposed in thevicinity of the crankshaft 8 in parallel therewith, are supported by theiron alloy bearing members 12, 12′ at at least one end portions thereof,the supporting rigidity of the balance shafts 22, 22′ can be enhanced.

Furthermore, since the upper end faces 12 f the bolt connecting portions12 c are positioned inwardly of each of the iron alloy bearing brackets12, 12′ so that the upper end faces 12 f are not exposed to thecylinder-side mating surface 2 e of the crankcase 2 in embedding theiron alloy bearing brackets 12, 12′ in the interior of the crankcase 2,there is no case where metallic members which are different in hardnessand material exist at the joint between the crankcase 2 and the cylinderblock 3 in an mixed fashion, and hence the reduction in sealingcapability can be avoided. Namely, in the event that the upper end face12 f of the iron alloy bolt connecting portion 12 c is brought intoabutment with the case-side mating surface 3 c formed on the lowerflange 3 b of the aluminum alloy cylinder body 3, the sealing capabilityis lowered due to the difference in thermal expansion coefficient or thelike.

In addition, since, in the left-side bearing bracket 12, the bearingcollar 12 d whose outside diameter is larger than balancer driving gear25 a is mounted on the outer circumferential surface of the bearing 11a, when assembling the crankshaft 8 in the crankcase 2 with the balancerdriving gear 25 a being mounted by way of press fit or the like to befixed thereto (or, there is, of course, no problem even in the eventthat the gear 25 a is formed as an integral part of the crankshaft 8),there is no risk that the balancer driving gear 25 a interferes with asmallest inside diameter portion of the boss portion 12 b of the bearingbracket 12, and hence the crankshaft 8 can be assembled properly withoutany problem.

The crankcase 2 is a two-piece type in which the crankcase 2 is dividedinto the left and right case portions 2 a, 2 b. A left case cover 9 isdetachably attached to the left case portion 2 a, and a space surroundedby the left case portion 2 a and the left case cover 9 constitutes aflywheel magnet compartment 9 a. A flywheel magnetic generator 35attached to the left end portion of the crankshaft 8 is accommodated inthis flywheel magnet compartment 9 a. Note that the flywheel magnetcompartment 9 a communicates with a camshaft arranging compartment viachain compartments 3 d, 4 d, which will be described later on, wherebymost of the lubricating oil which has been used to lubricate camshaftsfalls into the flywheel magnet compartment 9 a via the chaincompartments 3 d, 4 d.

In addition, a right case cover 10 is detachably attached to the rightcase portion 2 b, and a space surrounded by the right case portion 2 band the right case cover 10 constitutes a clutch compartment 10 a.

The crank compartment 2 c and a transmission compartment 2 d are formedat front and rear portions of the crankcase 2, respectively. The crankcompartment 2 c is made to open to the cylinder bore 3 a but is definedsubstantially to be separated from the other compartments such as thetransmission compartment 2 d. Due to this, the pressure within thetransmission compartment 2 d is caused to fluctuate as the pistonreciprocates vertically, thereby allowing the transmission compartment 2d to function as a pump.

The crankshaft 8 is arranged such that left and right arm portions 8 a,8 a and left and right weight portions thereof are accommodated in thecrank compartment 2 c. The crankshaft 8 is an assembly including a leftcrankshaft portion into which the left arm portion 8 a, weight portion 8b and shaft portion 8 c are integrated and a right crankshaft portioninto which the right arm portion 8 a, weight portion 8 b and shaftportion 8 c′ are integrated, the left crankshaft portion and the rightcrankshaft portion being connected integrally through a tubular crankpin 8 d.

The left and right shaft port-ions 8 c, 8 c′ are rotationally supportedon the left and right case portions 2 a, 2 b via the crankshaft bearings11 a, 11 a′. As has been described above, the bearings 11 a, 11 a′ arepress fitted in the bearing holes 12 a in the iron alloy bearingbrackets 12, 12′ which are insert cast in the left and right caseportions 2 a, 2 b of aluminum alloy.

A transmission 13 is accommodated and arranged in the transmissioncompartment 2 d. The transmission 13 is such as to have a constant meshconstruction in which a main shaft 14 and a drive shaft 15 are providedand arranged in parallel with the crankshaft 8, and first-speed tofifth-speed gears 1 p to 5 p attached to the main shaft 14 are made toconstantly mesh with first-speed to fifth-speed gears 1 w to 5 wattached to the drive shaft 15.

The main shaft 14 is rotationally supported by the left and right caseportions 2 a, 2 b via main shaft bearings 11 b, 11 b, whereas the driveshaft 15 is rotationally supported by 15 the left and right caseportions 2 a, 2 b via drive shaft bearings 11 c, 11 c.

A right end portion of the main shaft 14 passes through the right caseportion 2 b and protrudes to the right side, and a clutch mechanism 16is attached to the protruding portion, and this clutch mechanism 16 islocated within the clutch compartment 10 a. Then, a large reduction gear(an input gear) 16 a of the clutch mechanism 16 meshes with a smallreduction gear 17 fixedly attached to the right end portion of thecrankshaft 8.

A left end portion of the drive shaft 15 protrudes outwardly from theleft case portion 2 a and a driving sprocket 18 is attached to theprotruding portion. This driving sprocket 18 is connected to a drivensprocket on a rear wheel.

A balancer unit 19 according to the embodiment includes front and rearbalancers 20, 20′ disposed opposite across the crankshaft 8 and havingsubstantially the same construction. The front and rear balancers 20,20′ include the balance shaft 22, 22′ which do not rotate and weights24, 24 which are rotationally supported on the balance shat via bearings23, 23.

Here, the balance shafts 22, 22′ are made to double as the case bolts(the connecting bolts) for connecting the left and right case portions 2a, 2 b together in the direction in which the crankshaft extends. Therespective balance shafts 22, 22′ is also used to connect the left andright case portions together by causing flange portions 22 a formed oninsides of the rotationally supported weights 24 in a transversedirection of the engine to abut with outer end faces of boss portions 12g integrally formed on the bearing brackets 12′, 12 which are insertcast into the left and right case portions 2 a, 2 b and screwing fixingnuts 21 a, 21 b on opposite ends of the respective balance shafts.

The weight 24 includes a semi-circular weight main body 24 a and acircular gear supporting portion 24 b which is integrally formed on theweight main body, and a ring-shaped balancer driven gear 24 c is fixedlyattached to the gear supporting portion 24 b. Note that referencenumeral 24 b denotes a hole made in a part of the weight 24 which issituated opposite to the weight main body 24 a so as to reduce theweight of the part to as low a level as possible.

The balancer driven gear 24 c attached to the rear balancer 20′ mesheswith the balancer driving gear 25 a which is rotationally attachedrelative to the gear unit 25 which is securely attached to the leftshaft portion 8 c of the crankcase 8 through press fit.

Note that reference numeral 25 b denotes a timing chain driving sprocketintegrally formed on the gear unit 15 and has, as shown in FIG. 11, analigning or timing mark 25 c for alignment of timing marks for valvetiming. The gear unit 25 is press fitted on the crankshaft 8 such thatthe timing mark 25 c aligns with the cylinder bore axis A as viewed inthe direction in which the crankshaft extends when the crankshaft 8 issituated at a top dead center of a compression stroke.

In addition, the balancer driven gear 24 c attached to the frontbalancer 20 meshes with a balancer driving gear 17 a which is supportedrotationally relative to the small reduction gear 17 which is fixedlyattached to the right shaft portion 8 c′ of the crankshaft 8.

Here, the rear balancer driving gear 25 a is supported rotationallyrelative to the gear unit 25, and the front balancer driving gear 17 ais supported rotationally relative to the small reduction gear 17. Then,U-shaped damper springs 33 each made up of a plate spring are interposedbetween the balancer driving gears 25 a, 17 a and the gear unit 25 andthe small reduction gear 17, respectively, to thereby restrain thetransmission of impact generated due to a torque fluctuation occurringin the engine to the balancers 20, 20′ is restrained from beingtransmitted.

Here, while the balancer driving gear 17 a for driving the frontbalancer 20 will be described in detail by reference to FIG. 14, thesame description would be given if the balancer driving gear 25 a fordriving the rear balancer were described. The balancer driving gear 17 ais formed into a ring shape and is supported by a sliding surface 17 bformed so as to have a smaller diameter than the small reduction gear 17rotationally relative to a side of the small reduction gear 17. Then, anumber of U-shaped spring retaining grooves 17 c are formed in thesliding surface 17 b by setting them back into the surface thereof in aradial fashion about the center of the crankshaft, and the U-shapeddamper springs 33 are arranged to be inserted in place within the springretaining grooves 17 c. Opening side end portions 33 a, 33 a of thedamper spring 33 are locked at front and rear stepped portions formed ina locking recessed portion 17 d formed in an inner circumferentialsurface of the balancer driving gear 17 a.

When a relative rotation is generated between the small reduction gear17 and the balancer driving gear 17 a due to a torque fluctuation, thedamper springs 33 resiliently deform in a direction in which the spacebetween the end portions 33 a, 33 a narrows so as to absorb the torquefluctuation so generated. Note that reference numeral 17 g denotes acover plate for retaining the damper springs 33 within the retaininggrooves 17 c, reference numeral 17 h denotes a key for connecting thesmall reduction gear 1 with the crankshaft 8, and reference numerals 17e, 17 f denote, respectively, alignment marks for use in assembling thesmall reduction gear 17 and the balancer driving gear 17 a.

A mechanism for adjusting a backlash between the balancer driven gears24 c, 24 c and the balancer driving gears 25 a, 17 a is provided on thebalancers 20, 20′. This adjusting mechanism is constructed such that thebalancer axis of the balance shaft 22, 22′ slightly deviates from therotational center of the balancer driven gear 24 c. Namely, when thebalance shaft 22, 22′ is made to rotate about the balancer axis, thespace between the rotational center line of the balancer driven gear 24c and the rotational center line of the balancer driving gear 25 a, 17 achanges slightly, whereby the backlash is changed.

Here, a mechanism for rotating the balance shaft 22, 22′ differs betweenthe front balancer 20 and the rear balancer 20′. Firstly, in the rearbalancer 20′, a hexagonal locking protruding portion 22 b is formed on aleft end portion of the rear balance shaft 22′, and a spline-like (apolygonal star-like) locking hole 26 a formed in one end of a rotationallever 26 is locked on the locking protruding portion 22 b. In addition,an arc-like bolt hole 26 b is formed in the other end portion of therotational lever 26 in such a manner as to extend about the balanceraxis.

A fixing bolt 27 a passed through the bolt hole 26 b is planted in aguide plate 28. The guide plate 28 is generally formed into an arc-likeshape and is fixedly bolted to the crankcase 2. Note that the guideplate 28 has also a function to control the flow of lubricating oil.

The adjustment of the backlash of the rear balancer 20′ is implementedby rotating the rotational lever 26 so as to bring the backlash to anappropriate state with the fixing nut 21 a being loosened and thereafterby fixing the rotational lever 26 with the fixing bolt 27 a and a fixingnut 27 b, and thereafter, the fixing nut 21 a is refastened.

A grip portion 22 f having an oval cross section, which is formed byforming a flat portion 22 e on both sides of a cross-sectionallycircular shape, is formed on a left end portion of the front balanceshaft 22 (refer to FIG. 12). A collar 29 a having an innercircumferential shape which matches an outer circumferential shape ofthe grip portion 22 f is attached to the grip portion 22 f, andfurthermore, a holding portion 29 b of a holding lever 29 is attached toan outside of the collar 29 a in such a manner as to move axially but asnot to rotate relatively. A distal end portion 29 e of the holding lever29 is fixed to a boss portion 2 f of the left case portion 2 a with abolt 29 f. In addition, a tightening slit 29 c is formed in the holdingportion 29 b of the holding lever 29, so that the rotation of the collar29 and hence of the balance shaft 22 is prevented by tightening up thefixing bolt 29 d. Furthermore, the fixing nut 21 b is screwed on thebalance shaft 22 to an outer side of the collar 29 so as to be securedthereto via washer.

The adjustment of the backlash of the front balancer 20 is implementedby loosening the fixing nut 21 b or preferably removing the same,griping the grip portion 22 f of the balance shaft 22 with a tool torotate the shaft so as to bring the backlash to an appropriate state,and thereafter tightening up the fixing bolt 29 d, and thereafter, thefixing nut 21 b is fastened.

In addition, a lubricating oil introducing portion 22 c is formed in anupper portion of the locking protruding portion 22 b by cutting out theupper in an arc. A guide bore 22 d is made to open to the introducingportion 22 c, and the guide bore extends into the balance shaft 22 andpasses therethrough to below an outer circumferential surface of thebalance shaft 22, whereby the lubricating oil introducing portion 22 cis made to communicate with an inner circumferential surface of thebalancer bearing 23. Thus, lubricating oil that has fallen in thelubricating oil introducing portion 22 c is supplied to the balancerbearing 23.

Here, while the weight 24 and the balancer driven gear 24 c are disposedat the right end portion along the direction in which the crankshaftextends in the front balancer 20, in the rear balancer 20′, they aredisposed at the left end portion. In addition, the balancer driven gear24 c is located rightward relative to the weight 24 in both the frontand rear balancers 20, 20′, and therefore, the weight 24 and thebalancer driven gear 24 c are set into the same configuration in boththe front and rear balancers.

Thus, according to the embodiment, since the weight main body 24 a andthe balancer driven gear 24 c of the balancer 20 are disposed on theright-hand side (one side) of the front balance shaft (the primarybalance shaft) 22 along the direction in which the crankshaft extendsand the weight main body 24 a and the balancer driven gear 24 c aredisposed on the left-hand side (the other side) of the rear balanceshaft (the secondary balance shaft) 22′ along the direction in which thecrankshaft extends, the reduction in balance in weight in the crankshaftdirection that would result when providing a two-shaft balancer unit canbe avoided.

In addition, since the front and rear balance shafts 22, 22′ are made todouble as the case bolts for connecting the left and right case portions2 a, 2 b together, when adopting a two-shaft balancer unit, theconnecting rigidity of the crankcase can be enhanced while restrainingthe construction of the engine from becoming complex and the number ofcomponents from being increased.

Additionally, since the balancer weight main body 24 a and the balancerdriven gear 24 c are made integral and are supported rotationally by thebalance shafts 22, 22′, respectively, only the weight made up of thebalancer weight main body 24 a and the balancer driven gear 24 c may bedriven to rotate, and therefore, the engine output can be attempted tobe used effectively to such an extent that the balance shafts themselvesdo not need to be driven to rotate.

In addition, the degree of freedom in assembling can be improved whencompared with an engine construction in which a balancer weight and abalance shaft are made integral.

Additionally, since the rotational center lines of the balancer drivengears 24 c are caused to deviate relative to the axes of the balanceshafts 22, 22′, the backlash between the balancer driven gears 24 c andthe balancer driving gears 25 a, 27 a on the crankshaft 8 side can beadjusted by the simple construction or only by a simple operation ofrotating the balance shafts, thereby making it possible to prevent thegeneration of noise.

On the front balance shaft 22, the backlash adjustment is implemented bygripping the grip portion 22 f formed on the left-hand side of thebalance shaft 22 with a tool so as to rotate the balance shaft 22, andon the rear balance shaft 22′, the backlash adjustment is implemented byrotating the rotational lever 26 provided on the left-hand side of thebalance shaft 22′. Thus, on either of the front and rear balance shafts22, 22′, the backlash can be adjusted from the left-hand side of theengine, and hence the backlash adjusting work can be implementedefficiently.

Additionally, since the balancer driving gear 17 a on the crankshaft 8side which meshes with the balancer driven gear 24 c is constructed tobe disposed in such a manner as to rotate relatively to the slidingsurface 17 b of the small reduction gear 17 which is fixed to thecrankshaft 8 and the U-shaped damper springs 33 are disposed in thespring retaining grooves 17 c formed by setting them back from thesliding surface 17 b, the impact generated due to the torque fluctuationin the engine can be absorbed by the compact construction so that thebalancer unit can be operated smoothly. Note that the same descriptioncan be made with respect to the balancer drive gear 25 a.

Furthermore, a coolant pump 48 is disposed at the right end portion ofthe front balance shaft 22 coaxially therewith. A rotating shaft of thecoolant pump 48 is connected to the balance shaft 22 by an Oldham'scoupling which has a similar construction to that of a lubricating oilpump 52, which will be described later on, in such a manner that aslight deviation between the centers of the rotating shaft and thebalance shaft 22 can be absorbed.

In a valve train device of the embodiment, an intake camshaft 36 and anexhaust camshaft 37 which are disposed within the cylinder head cover 5are constructed to be driven to rotate by the crankshaft 8. To bespecific, a crankshaft sprocket 25 b of the gear unit 25 press fitted onthe left shaft portion 8 c of the crankshaft 8 so as to be attachedthereto and an intermediate sprocket 38 a rotationally supported by asupport shaft 39 planted in the cylinder head 4 are connected by atiming chain 40, and an intermediate gear 38 formed integrally on theintermediate sprocket 38 a and having a smaller diameter than that ofthe intermediate sprocket 38 a meshes with intake and exhaust gears 41,42 secured to end portions of the intake and the exhaust camshafts 36,37. Note that the timing chain 40 is disposed so as to pass through thechain compartments 3 d, 4 d formed on the left walls of the cylinderblock 3 and the cylinder head 4.

The intermediate sprocket 38 a and the intermediate gear 38 b arerotationally supported by the support shaft 39 which passes through thechain compartment 4 d on the cylinder head 4 in the direction in whichthe crankshaft extend along the cylinder bore axis A via two sets ofneedle bearings 44. The support shaft 39 is fixed at a flange portion 39a thereof to the cylinder head 4 with two bolts 39 b. Note thatreference numerals 39 c, 39 d denote a sealing gasket, respectively.

Here, commercially available (standard) bearings are adopted for the twosets of needle bearings 44, 44. A space adjusting collar 44 a isdisposed between the respective bearings 44, 44, and thrust washers 44b, 44 b for receiving thrust load are provided at ends of the bearings.The thrust washer 44 b is formed into a stepped shape having a largediameter portion which is brought into sliding contact with an end faceof the intermediate sprocket and a stepped portion which protrudesaxially toward the needle bearing 44.

Thus, since the space adjusting collar 44 a is interposed between thetwo sets of bearings 44, 44, commercially available standard bearingscan be adopted for the needle bearings by adjusting the length of thecollar 44 a, thereby making it possible to reduce costs.

In addition, since the washer having the stepped configuration isadopted as the thrust washer 44 b, the assembling work of theintermediate sprocket 38 a can be improved. Namely, in assembling theintermediate sprocket 38 a, while the support shaft 39 is inserted fromthe outside in a state in which the intermediate sprocket 38 a and theintermediate gear 38 b are disposed within the chain compartment 4 dwith the thrust washers being positioned at the ends of the intermediatesprocket 38 a and the intermediate gear 38 b in such a manner as not tofall therefrom, the thrust washer 44 b can be prevented from falling byallowing the stepped portion of the thrust washer 44 b to be locked in ashaft hole in the intermediate sprocket 38 a, and hence the assemblingproperties can be improved.

In addition, an oil hole 39 e is formed in the support shaft 39 forsupplying lubricating oil introduced from the cam compartment via an oilintroducing bore 4 e formed in the cylinder head 4 to the needle bearing44.

Additionally, four weight reduction holes 38 c and two inspection holes38 c adapted to be used at the time of assembling and made to double asweight reduction holes are formed at intervals of 60 degrees. Then, analignment or timing mark 38 d is stamped on a tooth situatedsubstantially at the center of the inspection hole 38 c′ for theintermediate gear 38 b, and timing marks 41 a, 42 a are also stamped ontwo teeth of intake and exhaust camshaft gears 41, 42 which correspondto the timing marks 38 d. Here, when aligning the left and right timingmarks 38 d, 38 d with the timing marks 41 a, 42 a, the intake andexhaust camshafts gears 41, 42 are located at positions, respectively,which correspond to a top dead center of a compression stroke.

Furthermore, timing marks 38 e, 38 e are also formed at portions of theintermediate sprocket 38 a which are situated on a cover side matingsurface 4 f of the cylinder head 4 when the timing marks 38 d align with41 a, 42 a.

To align valve timings, firstly, the crankshaft 8 is held at a top deadcenter of a compression stroke by aligning the timing mark 25 c (referto FIG. 11) with the cylinder bore axis A. In addition, the intermediatesprocket 38 a and the intermediate ear 38 b which are attached to thecylinder head 4 via the support shaft 39 are positioned so that thetiming mark 38 e of the intermediate sprocket 38 a aligns with the coverside mating surface 4 f, and in this state, the crankshaft sprocket 25 band the intermediate sprocket 38 a are connected by the timing chain 40.Then, the intake and exhaust camshaft gears 41, 42 on the intake andexhaust camshafts 36, 37 are brought into mesh engagement with theintermediate gear 38 b while confirming through the inspection hole 38c′ that the timing marks 41 a, 42 a align with the timing mark 38 d onthe intermediate gear 38 b, and the intake and exhaust camshafts 36, 37are fixed to an upper surface of the cylinder head 4 via cam carriers.

Thus, since the inspection holes 38 c′ made to double as the weightreduction holes to reduce the weight of the large diameter intermediatesprocket 38 a are provided in the intermediate sprocket 38 a, so thatthe alignment of the timing marks 38 d on the small diameterintermediate gear 38 b which is set on the back of the intermediatesprocket 38 a with the timing marks 41 a, 42 a on the camshaft gears 41,42 can be confirmed through the inspection holes 38 c′, the meshingpositions of the intermediate gear 38 b with the camshaft gears 41, 42can visually confirmed in an easy and ensured fashion while the smalldiameter intermediate gear 38 b is placed on the back of the largediameter intermediate sprocket 38 a, thereby making it possible to alignthe valve timings without any problem.

In addition, since the intermediate gear 38 b can be disposed on theback side of the intermediate sprocket 38 a, the dimension from thecamshaft gears 41, 42 which mesh with the intermediate gear 38 b to acam nose 36 a can be made shorter, whereby the torsional angle of thecamshaft can be made smaller to such an extent that the dimension ismade so shorter, thereby making it possible to make compact an areasurrounding the camshafts.

Namely, for example, in a case where the intermediate gear 38 b isdisposed on a front side of the intermediate sprocket 38 a, while thevalve timings can easily be aligned, the dimension from the camshaftgears 41, 42 to the cam nose becomes long, and the torsional angle ofthe camshafts becomes large to such an extent that the dimension isextended, thereby reducing the control accuracy of valve opening andclosing timings.

In addition, in a case where the intermediate gear 38 b is disposed infront of the intermediate sprocket 38 a, a space between theintermediate sprocket support shaft 39 and the camshafts 36, 37 needs tobe expanded in order to avoid any interference between the intermediatesprocket 38 a and the camshaft 36, 37, this causing a concern that thearea surrounding the camshafts is enlarged.

Here, a backlash adjusting mechanism is provided between theintermediate gear 38 b and the camshaft gears 41, 42. This adjustingmechanism has a construction in which the intake camshaft gear 41 andthe exhaust camshaft gear 42 are made up of two gears such as a drivinggear (a power transmission gear) 46 and a shift gear (an adjusting gear)45 and the angular positions of the driving gear 46 and the shift gear45 can be adjusted.

Namely, the shift gear 45 and the driving gear 46 are fixed to flangeportions 36 b, 37 b formed at end portions of the camshafts 36, 37,respectively, in such a manner that the angular positions thereof can beadjusted by four circumferentially long elongated holes 45 a, 46 a andfour long bolts 68 a. A clearance portion 46 b is cut and formed in thedriving gear 46 that is disposed outwardly, and only the shift gear 45is fixed in such a manner that the angular position thereof can beadjusted two elongated holes 45 b and two short bolts 68 b by making useof the clearance portion 46.

A backlash adjustment is implemented according to the followingprocedure. Note that in the engine according to the embodiment, theintermediate gear 38 b rotates counterclockwise as shown in FIG. 3 whenviewed from the left-hand side of the engine. Consequently, both theintake camshaft gear 41 and the exhaust camshaft gear 42 rotateclockwise. In addition, here, while the backlash adjustment will bedescribed with respect to the intake camshaft gear 41, the samedescription would be made with respect to the exhaust camshaft gear 42.

Firstly, all the fixing bolts 68 a, 68 b of the intake camshaft gear 41are loosened, and the shift gear 45 is rotated clockwise so that frontside surfaces of teeth of the shift gear 45 in the clockwise directionslightly abut with rear side surfaces of teeth of the intermediate gear38 b in the counterclockwise direction. In this state, the shift gear 45is fixed to the flange portion 36 b of the camshaft 36 with two shortbolts 68 b. Then, the driving gear 46 is rotated counterclockwise insuch a manner that front side surfaces (driven surfaces) of teeth of thedriving gear 46 in the counterclockwise direction abut with front sidesurfaces (driving surfaces) of the intermediate gear 38 b in thecounterclockwise direction so as to obtain a required backlash, and inthis state, four long bolts 68 a are tightened up, whereby the drivinggear 46 and the shift gear 45 are fixed to the intake camshaft 36.

Thus, since the intake and exhaust camshaft gears 41, 42 are made up ofthe driving gear (power transmission gear) 46 and the shift (adjustinggear) 45 adapted to rotate relatively to the driving gear, respectively,the backlash can be adjusted by rotating the shift gear 45 relatively tothe driving gear 46 forward or backward in the rotating directions.

Note that while, in this embodiment, both the driving gear 46 and theshift gear 45 which constitute the camshaft gears 41, 42 are describedas being able to rotate relatively to the camshafts, one of the drivinggear 46 and the shift gear 45 may be adapted to rotate relatively andthe other gear may be integrated into the camshaft. In this case, it isdesirable that the gear integrated into the camshaft constitutes thepower transmission gear. Even if constructed in this way, similarfunction and advantage to those obtained by the embodiment can beobtained.

In addition, while in the embodiment, the invention is described asbeing applied to the construction in which the chain drive method isadopted, the invention can of course be applied to a drive method usinga toothed belt.

Next, a lubricating construction will be described.

A lubrication system 50 of the engine according to the embodiment isconstructed such that lubricating oil stored within a separatelubricating oil tank 51 is picked up and pressurized by a lubricatingoil pump 52 via a down tube 56 c on a vehicle body frame, lubricatingoil discharged from the pump 52 is divided into three systems such as acam lubricating system 53, a transmission lubricating system 54 and acrank lubricating system 55 so as to be supplied to parts needing to belubricated at the respective systems, and lubricating oil used forlubricating the respective parts needing lubrication is returned to thelubricating oil tank 51 by making use of pressure fluctuation occurringwithin the crank compartment 2 c as the piston 6 reciprocatesvertically.

The lubricating oil tank 51 is formed integrally within a spacesurrounded by a head pipe 56 a, a main tube 56 b, the down tube 56 c anda reinforcement bracket 56 d of the vehicle body frame 56. Thislubricating oil tank 51 communicates with a cross pipe 56 e whichconnects lower portions of the down tube 56 c via the down tube 56 c.

Then, the cross pipe 56 e communicates with a pick-up port of thelubricating oil pump 52 via an outlet tube 56 f, an oil hose 57 a, ajoint pipe 57 b and a pick-up passageway 58 a formed in a crankcasecover 10. A discharge port of the lubricating oil pump 52 is connectedto an oil filter 59 via an oil discharge passageway 58 b, an externalportion connecting chamber 58 c and an oil passageway 58 d, whichconstitute a part of a lubricating oil passageway situated between thepump discharge port and the oil filter, and is divided into the threelubrication systems 53, 54, 55 on a secondary side of the oil filter 59.

The oil filter 59 is constructed such that an oil element 59 e isdisposed in a filter compartment 59 d defined by detachably attaching aportion of a cover body 47 which corresponds to a filter cover portion47 a to a filter recessed portion 10 b provided in the right case cover10 by setting part thereof further back from the rest. Note that thecover body 47 is an integral part including the filter cover portion 47a and a pump cover portion 47 b, which will be described later on.

The cam lubricating system 53 has a construction which is generallyconstructed such that a lower end of a vertical member 53 a of aT-shaped lubricating oil pipe is connected to a cam side outlet 59 a ofan oil passageway formed the filter cover portion 47 a to the outside ofthe filter recessed portion lob, whereas left and right ends of ahorizontal member 53 b of the lubricating oil pipe are connected to acamshaft oil supply passageway 53 c, so that lubricating oil is suppliedto parts such as bearings of camshafts 36, 37 which need to belubricated via the passageway 53 c.

The transmission lubrication system 54 has the following construction. Aright transmission oil supply passageway 54 a formed within the rightcase portion 2 b is connected to a transmission side outlet 59 b of theoil filter 59, and the oil supply passageway 54 a communicates with theinterior of a main shaft bore 14 a formed in the main shaft 14 along theaxial center thereof via a left transmission oil passageway 54 b formedin the left case portion 2 a. Then, this main shaft bore 14 acommunicates with sliding portions between the main shaft 14 andchange-speed gears via a plurality of branch bores 14 b, wherebylubricating oil supplied to the main shaft bore 14 a passes through thebranch bores 14 b to be supplied to the sliding portions.

In addition, an intermediate portion of the left transmission oilpassageway 54 b communicates with a bolt bore 60 a through which a casebolt 60 for connecting the left and right case portions 2 a, 2 btogether is allowed to pass. This bolt bore 60 a is such as to be formedby forming a bore having an inside diameter which is slightly largerthan the outside diameter of the case bolt 60 in tubular boss portions60 c, 60 c which are formed so as to face and abut with each other onthe mating surface between the left and right case portions 2 a, 2 b.The boss portion 60 c is situated in the vicinity of a portion where agear train on the main shaft 14 meshes with a gear train on the driveshaft 15, and a plurality of branch bores 60 b are formed from whichlubricating oil within the bolt bore 60 a is spouted out toward the geartrains meshing portion. Note that the bolts 60 shown in FIG. 19 as beingdeveloped into the left and right case portions are the same bolt.

Furthermore, a right end portion of the bolt bore 60 a communicates witha drive shaft bore 15 a formed in the drive shaft 15 along the axialcenter thereof via a communication bore 54 c. Then, the drive shaft bore15 a is closed by a partition wall 15 c at a left-hand side portion andcommunicates with sliding portions between the drive shaft 15 anddriving gears via a plurality of branch bores 15 b. Thus, lubricatingoil supplied into the drive shaft bore 15 a passes through the branchbores 15 b to be supplied to the sliding portions.

The crank lubricating system 55 has the following construction. A crankoil supply passageway 55 a, which is formed in the cover body 47 as partof the lubricating oil passageway which is situated between the oilfilter and the lubricating oil passageway in such a manner as to extendfrom a crank side outlet 59 c toward the lubricating oil pump 52, ismade to communicate with a communication bore (a in-pump oil supplypassageway) 62 a which is formed in a rotating shaft 62 of thelubricating oil pump 52 to pass therethrough along the axial centerthereof, and furthermore, the communication bore 62 a communicates witha crank oil supply bore (a in-crankshaft oil supply passageway) 8 eformed in the crankshaft 8 to pass therethrough along the axial centerthereof via a connecting pie 64. Then, this crank oil supply bore 8 ecommunicates with the interior of a pin bore 65 a in a crank pin 65 viaa branch bore 8 f, and the pin bore 65 a is made to open to the rotatingsurface of a needle bearing 7 b at a big end portion 7 a of a connectingrod 7 via a branch bore 65 b. Thus, lubricating oil filtered in the oilfilter 59 is supplied to the rotating surface of the needle bearing 7 b.

The lubricating oil pump 52 is fitted and mounted in a pump supportinghole 10 b formed in the right-side case cover 10 and is covered with thepump cover portion 47 b of the cover body 47 which is detachablyattached to the right-side case cover 10.

The lubricating oil pump 52 has a construction which is generallyconstructed such that a pump compartment 61 c is provided in a rightcase 61 b of a two-piece casing made up of left and right cases 61 a, 61b in such a manner as set a relevant portion of the case further backfrom the rest, a rotor 63 is disposed rotationally within the pumpcompartment 61, the pump shaft 62 is inserted into the rotor 63 alongthe axial center thereof in such a manner as to pass therethrough andthe pump shaft 62 and the rotor 63 are fixed together with a pin 63 a.Note that an oil pick-up passageway 58 a and an oil discharge passageway58 b are connected to a pump compartment upstream side and a pumpcompartment downstream side of the left case 61 a, respectively.

In addition, the oil pick-up passageway 58 a and the crank oil supplypassageway 55 a which is the lubricating oil passageway situated betweenthe oil filter and the lubricating oil pump are made to communicate witheach other via a pressure regulating relief valve 66 which is interposedtherebetween. This relief vale 66 is such as to maintain the dischargepressure of the lubricating oil pump 52 at a predetermined value or lessand has a construction in which the crank oil supply passageway 55 a andthe oil pick-up passageway 58 a are made to communicate with each othervia a pipe 66 a, an opening of the pipe 66 a which is situated at an endthereof facing the oil pick-up passageway is adapted to be opened andclosed by a ball valve 66 b and the ball valve 66 b is press biasedtoward a closing direction by a biasing spring 66 c.

When the pressure on the discharge side of the lubricating oil pump 52reaches or exceeds the predetermined value, the ball valve 66 b opensthe pipe 66 a against the spring force of the biasing spring 66 c so asto relieve the pressure on the crank oil supply passageway side to theoil pick-up passageway 58 a side, whereby the discharge side pressure ofthe lubricating oil pump 52 is regulated to the predetermined value.

The pump shaft 62 is a tubular shaft which passes through the pump case61 in the axial direction and opens to the crank oil supply passageway55 a at a right end portion thereof as shown in the drawing. Inaddition, a power transmitting flange portion 62 b is formed integrallyat a left end portion of the rotating shaft 62 as shown in the drawing.The flange portion 62 b faces a right end face of the crankshaft 8, andthe flange portion 62 b and the crankshaft 8 are connected together byan Oldham's coupling 67 in such a manner as to absorb a slight deviationof the centers of the shafts.

To describe in detail, the Oldham's coupling 67 is constructed such thata coupling plate 67 a is disposed between the crankshaft 8 and theflange portion 62 b, a pin 67 c planted in the flange portion 62 b isinserted into a connecting bore 67 d in the coupling plate 67 a and apin 67 b planted in the end face of the crankshaft 8 is inserted into aconnecting bore 67 e.

In addition, the connecting pipe 64 is such as to connect the right endopening of the oil supply passageway within the crankshaft 8 to the leftend opening of the oil supply passageway within the pump shaft 62, andsealing is provided by an oil seal 64 a between the inner circumferenceof the crankshaft side opening and the inner circumference of the pumpshaft side opening and the outer circumference of the connecting pipe64.

Thus, with the lubrication system according to the embodiment, since thelubricating oil pump 52 is disposed so as to be connected to the one endof the crankshaft 8 and the discharge port of the lubricating oil pump52 is made to communicate with the crank oil supply bore (thein-crankshaft oil supply passageway) 8 e formed within the crankshaft 8via the communication bore (the in-pump oil supply passageway) 62 aformed within the pump shaft 62 of the lubricating oil pump 52 and theconnecting pipe 64, the lubricating oil can be supplied to the parts ofthe crankshaft 8 which need to be lubricated by the simple and compactconstruction.

In addition, since the crankshaft 8 and the lubricating oil pump 52 areconnected together by the Oldham's coupling 67 which can absorb thedisplacement of the shafts in the direction normal thereto and thecommunication bore 62 a and the crank oil supply bore 8 e are made tocommunicate with each other via the connecting pipe 64 with the O rings64 a having elasticity being interposed between the connecting pipe 64and the communicating bore 62 a, the crank oil supply bore 8 e, even inthe event that the centers of the crankshaft 8 and the pump shaft 62 arecaused to deviate slightly from each other, lubricating oil can besupplied to the parts needing to be lubricated without any problem,thereby making it possible to secure the required lubricatingproperties.

Additionally, since the lubricating oil pump is detachably attached tothe crankcase cover 10 and is covered with the pump cover portion 47 bof the cover body 47 detachably attached to the crankcase cover 10, theconstruction in which the lubricating oil pump 52 is disposed within thecrankcase so as to supply lubricating oil to the in-crankshaft oilsupply passageway can be realized by the simple and compactconstruction.

Furthermore, since the discharge port of the lubricating oil pump 52 andthe oil supply passageway within the pump shaft are made to communicatewith each other via the lubricating oil passageway, the oil filter 59can easily be interposed at the intermediate position along the lengthof the lubricating oil passageway, thereby making it possible to avoid aproblem that the disposition of an oil filter becomes difficult in theevent that the discharge port of the lubricating oil pump is made tocommunicate directly with the in-crankshaft oil supply passageway.

In addition, since the oil filter 59 is constructed such that the oilelement 59 a is disposed within the filter compartment 59 d defined bythe crankcase cover 10 and the filter cover portion 47 a of the coverbody 47 which is detachably attached to the crankcase cover 10, the oilfilter 59 can be disposed on the discharge side of the lubricating oilpump 52 by the simple construction, so that the required lubricatingperformance can be secured for a long period of time. In addition, oilelements 59 e can be replaced only by removing the cover body 47, thisfacilitating the maintenance of the oil filter 59.

Additionally, since the part between the lubricating oil pump dischargeport and the oil filter is formed in the crankcase cover 10 and the partbetween the oil filter and the in-pump passageway is formed in the coverbody (the filter cover portion) 47, the complex lubricating passagewaywhich extends upwardly from the lubricating oil pump once and thenreturns downwardly can be realized by the simple construction.

In addition, since the filter cover portion 47 a and the pump coverportion 47 b are formed as the integral parts of the cover body 47, theconstruction can be simplified, and the cover body 47 can be attachedand detached by removing several attachment bolts, whereby maintenancework can be facilitated.

Furthermore, since the pressure regulating relief valve 66 is interposedbetween the passageway 58 a on the pick-up side of the lubricating oilpump 52 and the part of the lubricating oil passageway which is situatedbetween the oil filter and the pump, the lubricating oil pump dischargeside pressure can be regulated to the predetermined pressure by thesimple construction.

Here, as has been described above, the crank compartment 2 c is definedseparately from the other transmission compartment 2 d, the flywheelmagnet compartment 9 a and the clutch compartment 10 a, whereby an oilreturn mechanism is constructed in which the pressure within the crankcompartment 2 c is fluctuated to be positive and negative in conjunctionwith the reciprocating motion of the piston 6, so that lubricating oilin the respective compartments is returned to the lubricating oil tank51 by virtue of the pressure fluctuation.

To describe this in detail, a discharge port 2 g and a suction orpick-up port 2 h are formed in the crank compartment 2 c. A dischargeport reed valve 69 adapted to open when the pressure within the crankcompartment is positive is disposed in the discharge port 2 g, and apick-up port reed valve 70 adapted to open when the pressure within thecrank compartment is negative is disposed in the pick-up port 2 h.

Then, the discharge port 2 g communicates with the clutch compartment 10a from the crank compartment 2 c via a communication bore 2i and thencommunicates with the transmission compartment 2 d from the clutchcompartment 10 a via a communication bore 2 j. Furthermore, thetransmission compartment 2 d communicates with the flywheel magnetcompartment 9 a via a communication bore 2 k. A return port 2 m formedso as to communicate with the flywheel magnet compartment 9 acommunicates with the lubricating oil tank 51 via a return hose 57 c, anoil strainer 57 d and a return hose 57 e.

Here, a guide plate 2 n is provided at the return port 2 m. This guideplate 2 n has a function to ensure the discharge of lubricating oil bymodifying the return port 2 m so as to provide a narrow gap a between abottom plate 2 p and itself and to secure a wide width b.

In addition, an oil separating mechanism is connected to the lubricatingoil tank 51 for separating oil mists contained in the air within thetank by virtue of centrifugal force so as to return oil mists soseparated to the crank compartment 2 c. This oil separating mechanismhas a construction in which an introduction hose 72 a which is connectedto an upper portion of the lubricating oil tank 51 at one end thereof istangentially connected to an upper portion of a cone-shaped separatingcompartment 71 at the other end and a return hose 72 b connected to abottom portion of the separating compartment 71 is connected to thepick-up port 2 h of the crank compartment 2 c. Note that the air fromwhich the oil mists are separated is discharged to the atmosphere via anexhaust hole 72 c.

Thus, according to the embodiment, since the crank chamber 2 c is madeto be a substantially closed space so that the pressure thereinfluctuates as the piston 6 reciprocates vertically, whereby lubricatingoil that has flowed into the crank compartment 2 c is sent back to thelubricating oil tank 51 by virtue of pressure fluctuation within thecrank compartment 2 c, the necessity of an exclusive oil sending pump (ascavenging pump) can be obviated, and hence the construction of theengine can be simplified and costs can be attempted to be reduced.

In addition, since the discharge port reed valve (an outlet side checkvalve) 69 adapted to open when the pressure in the crank compartmentincreases and to close when the pressure lowers is disposed in thevicinity of where the oil sending passageway is connected to the crankcompartment 2 c, the lubricating oil within the crank compartment 2 ccan be sent back to the lubricating oil storage tank 51 in a moreensured fashion.

In addition, since an portion above the oil level within the lubricatingoil storage tank 51 is connected to the crank compartment 2 via thereturn hoses 72 a, 72 b and the discharge port reed valve (a pick-upside check valve) 70 adapted to open when the pressure in the crankcompartment 2 c lowers and to close when the pressure increases isprovided in the vicinity where the return hoses are connected to thecrank compartment 2 c, air required is picked up into the crankcompartment 2 c when the piston 6 moves upwardly, whereas the insidepressure of the crank compartment 2 c increases as the piston 6 lowers,whereby lubricating oil within the crank compartment 2 c can be senttout in a more ensured fashion.

Incidentally, in a case where there is provided no air supply path fromthe outside to the interior of the crank compartment 2 c, only anegative pressure or a lower positive pressure is formed inside thecrank compartment, this causing a concern that there occurs a case whereoil cannot be sent out properly.

Furthermore, since the centrifugal lubricating oil mist separatingmechanism 71 for separating lubricating oil mist is interposed at theintermediate position along the length of the return passageways 72 a,72 b, so that lubricating oil mist so separated is returned to the crankcompartment 2 c via the return hose 72 b, whereas air from which themist content is removed is discharged to the atmosphere, onlylubricating oil mist can be returned to the crank compartment, wherebythe reduction in oil sending efficiency can be avoided which would occurwhen an excessive amount of air is allowed to flow into the crankcompartment, thereby making it possible to send out lubricating oil inthe crank compartment in an ensured fashion while preventing theatmospheric pollution.

Furthermore, since the tubular boss portion 60 c is formed in thevicinity of the main shaft 14 and the drive shaft 15 which constitutethe transmission, the crankcase connecting case bolt 60 is inserted intothe bolt bore 60 a in the boss portion 60 c so that the space betweenthe inner circumferential surface of the bolt bore 60 a and the outercircumferential surface of the case bolt 60 is made to form thelubricating oil passageway, and the branch bore (the lubricating oilsupply bore) 60 b is formed which is directed to the change-speed gearsat the boss portion 60 c, lubricating oil can be supplied to the meshingsurfaces of the change-speed gears while obviating the necessity ofproviding an exclusive lubricating oil supply passageway.

In addition, since the other end of the lubricating oil passagewaydefined by the inner circumferential surface of the bolt bore 60 c andthe outer circumferential surface of the case bolt 60 is made tocommunicate with an opening of the drive shaft bore (the lubricating oilpassageway) 15 a formed within the drive shaft 15 which is situatedopposite to an outlet side of the bore, lubricating oil can be suppliedto the portions on the drive shaft 15 which are brought into slidingcontact with the change-speed gears while obviating the necessity ofproviding an exclusive lubricating oil supply passageway.

Industrial Applicability

According to the first aspect of the invention, since the pump shaft ofthe lubricating oil pump is connected to the end of the crankshaft,there is no risk that the oscillation of the crankshaft is transmitteddirectly to the pump side that would occur in a case where the innerrotor of the lubricating oil pump is attached directly to thecrankshaft, and hence the lubricating oil pump can be disposed at theposition axially spaced away from the bearing portions of thecrankshaft, thereby making it possible to enhance the degree of freedomin selecting where to dispose the lubricating oil pump.

In addition, since the other end of the in-pump oil supply passageway ismade to communicate with the discharge port of the lubricating oil pumpvia the lubricating oil passageway, for example, the oil filter can beinterposed, as required, at the intermediate position along the lengthof the lubricating oil passageway, there by making it possible toenhance the degree of freedom in design when compared with theconventional example in which the discharge port of the lubricating oilpump is made to communicate directly with the in-crankshaft oil supplypassageway.

Additionally, according to the second aspect of the invention, since thepump shaft and the crank shaft are connected together by the couplingwhich can absorb the displacement of the shafts in the direction normalthereto, and the in-pump oil supply passageway in the pump shaft and thein-crankshaft oil supply passageway are made to communicate with eachother by interposing the connecting pipe between the pump shaft and thecrankshaft, lubricating oil can be supplied to the parts needing to belubricated without any problem even in case the centers of the pumpshaft and the crankshaft are caused to slightly deviate from each other,thereby making it possible to secure the required lubricatingproperties.

According to the third aspect of the invention, since the lubricatingoil pump is detachably attached to the crankcase cover and is thencovered with the pump cover which is detachably attached to thecrankcase cover, the lubricating oil pump can be disposed andlubricating oil can be supplied to the in-crankshaft oil supplypassageway by the simple construction.

According to the fourth aspect of the invention, since the oil filter isinterposed at the intermediate position along the length of thelubricating oil passageway and the oil filter so interposed isconstructed such that the element is disposed within the filtercompartment defined by the crankcase cover and the filter cover which isdetachably attached to the crankcase cover, the oil filter can bedisposed on the discharge side of the lubricating oil pump so as tosecure the required lubricating performance for a long period of time bythe simple construction.

In addition, since the part of the lubricating oil passageway that issituated between the lubricating oil pump discharge port and the oilfilter is formed in the crankcase cover and the part situated betweenthe oil filter and the in-pump oil passageway is formed in the filtercover, the lubricating oil passageway that would otherwise be complexcan be realized in the simple construction.

According to the fifth aspect of the invention, since the pump cover andthe filter cover are formed integrally, the construction can besimplified further.

According to the sixth aspect of the invention, since the pressureregulating relief valve is interposed between the passageway on thepick-up side of the lubricating oil pump and the lubricating oilpassageway situated downstream of the oil filter, the lubricating oilpump discharge side pressure can be regulated to the predeterminedpressure by the simple construction.

1. An engine lubrication system having a lubricating oil pump that isrotationally driven by a crankshaft to send under pressure a lubricatingoil to a part needing to be lubricated, characterized in that thelubricating oil pump is disposed so as to be connected to an end of acrankshaft in such a manner that a pump shaft aligns with the crankshaftsubstantially coaxially, in that an in-pump oil supply passageway isformed in the lubricating oil pump in such a manner as to passtherethrough from a side opposite to the crankshaft to a side of thecrankshaft, and in that the in-pump oil supply passageway so formed ismade to communicate at one end thereof with an in-crankshaft oil supplypassageway formed in the crankshaft for supplying a lubricating oil to apart of the crankshaft which needs to be lubricated and is made tocommunicate at the other end thereof with a discharge port of thelubricating oil pump via a lubricating oil passageway.
 2. An enginelubrication system as set forth in claim 1, characterized in that thein-pump oil supply passageway is formed in the pump shaft, in that thepump shaft and the crankshaft are connected together with a couplingwhich can absorb a displacement of the shafts in a direction normalthereto, in that a connecting pipe is interposed between the pump shaftand the crankshaft in such a manner as to absorb the displacement of theshafts in the direction normal thereto, and in that the in-crankshaftoil supply passageway and the in-pump oil supply passageway are made tocommunicate with each other by the connecting pipe.
 3. An enginelubrication system as set forth in claim 1 or 2, characterized in thatthe lubricating oil pump is attached to a crankcase cover detachably andis covered with a pump cover that is attached to the crankcase coverdetachably.
 4. An engine lubrication system as set forth in claim 3,characterized in that an oil filter is provided at an intermediateposition along the length of the lubricating oil passageway, in that theoil filter is constructed such that an element is disposed in a filtercompartment defined by the crankcase cover and a filter cover attachedto the crankcase cover detachably, in that a part of the lubricating oilpassageway situated between the discharge port of the lubricating oilpump and the oil filter is formed on the crankcase cover, and in that apart of the lubricating oil passageway situated between the oil filterand the in-pump passageway is formed on the filter cover which coversthe oil filter detachably.
 5. An engine lubrication system as set forthin claim 4, characterized in that the pump cover and the filter coverare integrally formed.
 6. An engine lubrication system as set forth inclaim 5, characterized in that a passageway on a pick-up side of thelubricating oil pump and a part of the lubricating oil passageway thatis situated on a downstream side of the oil filter are made tocommunicate with each other via a pressure regulating relief valve.